zfs: dataset is busy

[Gerrit Kühn]

Hi all,

I have several machines here that do automatic snapshotting via RSEs
snapshot-tool (sysutils/freebsd-snapshot). I use a homemade script to
incrementally transfer daily snapshots to a backup server. This runs fine
with machines running 7.0-STABLE of Jun 08.
However, I have one box with 7.1-PRERELEASE from Sep 08 showing the
following error after some time (when trying to rotate the snapshots via
the freebsd-snapshot tool):

cannot destroy 'tank/www at daily.6': dataset is busy


I fact I cannot do anything to the snapshot, neither destroy nor export
(not even with "-f"), it is always "busy". The only chance to get away
from this I found is to reboot the machine. After a reboot it is fine for
some weeks, but then comes back with the same problem.

Has anyone seen this before? Is there a fix or workaround available? Are
there any improvements I could take profit of by upgrading to 7.2-stable?
Right now the machine is in this state, so I could get some more
information from it (if anyone tells me what to do :-).


cu
  Gerrit